Strangers in The Night
The midnight train is coming down the Strujen-Bajen mountains. Art Farnanski seems to be dozing off in his seat.
Someone knows that this is not true.
At the station, all the passengers get off the train, except one. The conductor comes and taps him on the shoulder to let him know they have arrived. Art Farnanski does not answer, He is dead.
"His heart?" asks Commander Abrojos, looking at the dead body.
"Strychnine," answers the forensic doctor.
Hours later, the four people that had shared the train compartment with the dead man are at the police station.
The man in the dark suit:
"I'm innocent. The blonde woman was talking to Farnanski."
The blonde woman:
"I'm innocent. I did not speak to Farnanski."
The man in the light suit:
"I'm innocent. The brunette woman killed him."
The brunette woman:
"I'm innocent. One of the men killed him."
The same morning, while he is serving him coffee, the waiter at the Petit Piccolo asks commander Abrojos:
"This is an easy case for you, isn't it?"
"Yes," answers the commander. "Four true statements and four false one. Easy as pie."
Who killed Farnanski? (Only one person is guilty.)
The blond woman killed Mr. Farnanski. There are only four true statements. Only one person is guilty. Therefore, three of the "I'm innocent" statements are true. Only one more statement can be true, and this must be the one made by the man in the dark suit or by the blonde woman. Therefore, "The brunetter killed him" and "One of the men killed him" are false statements, so the blonde woman is the killer.
Courtesy: Mensa Mind Challenges Book.